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Abstract

Purple loosestrife is a noxious weed quickly invading Nebraska's wetlands. This publication describes the rearing and releasing of insects for biological control of the weed, as one part of an integrated management program.

Purple loosestrife is a noxious perennial weed invading thousands of acres of wetlands and waterways in the Midwest. In Nebraska an estimated 18,000 acres are already infested by this plant, mostly along the main rivers and waterways. It has no natural enemies in North America, therefore it is very hard to prevent it from spreading. For years people have tried to eradicate it, especially in the Great Lakes region and northeastern United States. Now it is clear that this is impossible and we must find ways to live with this plant. The challenge in our state is to contain the weed and stop its spread.

Bio-control agents can be an important component of an integrated approach to stop the expansion of purple loosestrife in Nebraska. They are especially valuable for those sites that are not easily accessible for other methods of control.

At some sites loosestrife covers 95 percent of the wetland while growing under large trees, which prevents the use of other control methods, especially aerial application of selective herbicides. Control of such sites is limited to biocontrol agents and would benefit from the establishment of local insectariums for rearing and releasing biocontrol insects. Several insect species were introduced from Europe, where loosestrife originated. They include: root weevil (Hylobius sp.), two beetles (Galerucella pusilla and G. calmariensis), and two flower-feeding weevils (Nanophyes sp.). Based on the quarantine studies conducted by USDA, these insects are highly host specific to purple loosestrife, defoliating the plant as both adults and larvae. These insects, in combination with other plant species, act as natural competitors to keep loosestrife under control in Europe.